Physical layer frame format for WLAN

ABSTRACT

A first field of a preamble of a physical layer (PHY) data unit is generated to include a first set of one or more information bits indicating a duration of the data unit and is formatted to conform to a first communication protocol such that the first field allows a receiver device conforming to a second communication protocol to determine the duration of the data unit. A second field of the preamble is generated to include a second set of one or more information bits indicating to a receiver device conforming to the first communication protocol that the data unit conforms to the first communication protocol. The second field is convolutionally coded using a tail biting technique, and the first field and the second field are modulated using a modulation scheme specified for a field corresponding to the first field and the second field, respectively, by the second communication protocol.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/274,475, entitled “Physical Layer Frame Format for WLAN,” filed May9, 2014, which claims the benefit of U.S. Provisional Patent ApplicationNo. 61/821,947, entitled “Physical Layer Frame Format for WLAN,” filedMay 10, 2013. The disclosures of the applications referenced above arehereby expressly incorporated herein by reference in their entireties.

This application is also related to U.S. patent application Ser. No.13/856,277, entitled “Physical Layer Frame Format for WLAN,” filed Apr.3, 2013, now U.S. Pat. No. 9,131,528, the disclosure of which is herebyexpressly incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to provideeven greater throughputs, such as throughputs in the tens of Gbps range.

SUMMARY

In an embodiment, a method is for generating a physical layer (PHY) dataunit for transmission via a communication channel, the PHY data unitconforming to a first communication protocol. The method includesgenerating, at a communication device, a first field to be included in apreamble of the PHY data unit. The first field includes a first set ofone or more information bits that indicate a duration of the PHY dataunit, and is formatted such that the first field is decodable by areceiver device that conforms to a second communication protocol, butdoes not conform to the first communication protocol, to determine theduration of the PHY data unit based on the first field. The method alsoincludes generating, at the communication device, a second field to beincluded in the preamble. The second field includes a second set of oneor more information bits that indicate to a receiver device thatconforms to the first communication protocol that the PHY data unitconforms to the first communication protocol. Generating the secondfield includes one or both of (i) generating the second set of one ormore information bits according to an error detection scheme notspecified by the second communication protocol and (ii) generating thesecond set of one or more information bits to indicate a mode notsupported by the second communication protocol. The method furtherincludes: modulating, at the communication device, the first field usinga modulation scheme specified for a field corresponding to the firstfield by the second communication protocol; convolutionally coding, atthe communication device, the second field using a tail bitingtechnique; modulating, at the communication device, the convolutionallycoded second field using a modulation scheme specified for a field,which corresponds to the second field, by the second communicationprotocol; generating, at the communication device, the preamble toinclude at least the first field and the second field; and generating,at the communication device, the PHY data unit to include at least thepreamble.

In another embodiment, an apparatus comprises a network interface devicehaving one or more integrated circuits. The one or more integratedcircuits are configured to generate a first field to be included in apreamble of a physical layer (PHY) data unit. The first field includes afirst set of one or more information bits that indicate a duration ofthe PHY data unit, and is formatted such that the first field isdecodable by a receiver device that conforms to a second communicationprotocol, but does not conform to the first communication protocol, todetermine the duration of the PHY data unit based on the first field.The one or more integrated circuits are also configured to generate asecond field to be included in the preamble. The second field includes asecond set of one or more information bits that indicate to a receiverdevice that conforms to the first communication protocol that the PHYdata unit conforms to the first communication protocol. Generating thesecond field includes one or both of (i) generating the second set ofone or more information bits according to an error detection scheme notspecified by the second communication protocol and (ii) generating thesecond set of one or more information bits to indicate a mode notsupported by the second communication protocol. The one or moreintegrated circuits are further configured to: modulate the first fieldusing a modulation scheme specified for a field corresponding to thefirst field by the second communication protocol; convolutionally codethe second field using a tail biting technique; modulate theconvolutionally coded second field using a modulation scheme specifiedfor a field, which corresponds to the second field, by the secondcommunication protocol; generate the preamble to include at least thefirst field and the second field; and generate the PHY data unit toinclude at least the preamble.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment.

FIGS. 2A and 2B are diagrams of a prior art data unit format.

FIG. 3 is a diagram of another prior art data unit format.

FIG. 4 is a diagram of another prior art data unit format.

FIG. 5 is a diagram of an example data unit format, according to anembodiment.

FIG. 6A is a set of diagrams of modulation used to modulate symbols in aprior art data unit.

FIG. 6B is a set of diagrams of modulation used to modulate symbols inan example data unit, according to an embodiment.

FIG. 7A is a diagram of an example data unit format, according to anembodiment.

FIG. 7B shows diagrams of modulation used to modulate symbols in thedata unit depicted in FIG. 7A, according to an embodiment.

FIGS. 8A-8G are diagrams of example bit allocations for a signal field,according to an embodiment.

FIGS. 9A-9C are diagrams depicting several example cyclic redundancycheck (CRC) generation schemes, according to several embodiments.

FIG. 10 is a block diagram depicting a detection scheme for detectingwhether a data unit conforms to a first communication protocol or to asecond communication protocol, according to an embodiment.

FIG. 11 is a block diagram depicting another detection scheme fordetecting whether a data unit conforms to a first communication protocolor to a second communication protocol, according to an embodiment.

FIG. 12 is a block diagram depicting yet another detection scheme fordetecting whether a data unit conforms to a first communication protocolor to a second communication protocol, according to an embodiment.

FIG. 13A is a diagram of an example data unit format, according to anembodiment.

FIG. 13B is a set of diagrams of modulation used to modulate symbols inthe data unit depicted in FIG. 13A, according to an embodiment.

FIG. 14A is a diagram of an example data unit format, according to anembodiment.

FIG. 14B is a set of diagrams of modulation used to modulate symbols inthe data unit depicted in FIG. 14A, according to an embodiment.

FIG. 15A is a block diagram of an example transmitter according to anembodiment.

FIG. 15B is a block diagram of a receiver according to an embodiment.

FIG. 16 is a diagram of a method for generating a data unit, accordingto an embodiment.

FIG. 17 is a diagram of a method for detecting whether a data unitconforms to a first communication protocol or to a second communicationprotocol, according to an embodiment.

FIG. 18 is a diagram of a method for generating a data unit, accordingto an embodiment.

FIG. 19A is a diagram of an example data unit format, according to anembodiment.

FIG. 19B is a diagram of an example data unit format, according to anembodiment.

FIG. 20A is a diagram of an example data unit format, according to anembodiment.

FIG. 20B is a diagram of an example data unit format, according to anembodiment.

FIG. 21A is a diagram of an example data unit format, according to anembodiment.

FIG. 21B is a diagram of an example data unit format, according to anembodiment.

FIG. 22A is a diagram of an example data unit format, according to anembodiment.

FIG. 22B is a diagram of an example data unit format, according to anembodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. The AP is configured to operatewith client stations according to at least a first communicationprotocol. The first communication protocol, according to someembodiments, is referred herein as “ultra high throughput” or “UHT”communication protocol. In some embodiments, different client stationsin the vicinity of the AP are configured to operate according to one ormore other communication protocols which define operation in the samefrequency band as the UHT communication protocol but with generallylower data throughputs. The lower data throughput communicationprotocols (e.g., IEEE 802.11a, IEEE 802.11n, and/or IEEE 802.11ac) arecollectively referred herein as “legacy” communication protocols. Whenthe AP transmits a data unit according to the UHT communicationprotocol, a preamble of the data is formatted such that a client stationthat operates according to a legacy protocol, and not the UHTcommunication protocol, is able to determine certain informationregarding the data unit, such as a duration of the data unit, and/orthat the data unit does not conform to the second protocol.Additionally, a preamble of the data unit is formatted such that aclient station that operates according to the UHT protocol is able todetermine the data unit conforms to the UHT communication protocol.Similarly, a client station configured to operate according to the UHTcommunication protocol also transmits data units such as describedabove.

In at least some embodiments, data units formatted such as describedabove are useful, for example, with an AP that is configured to operatewith client stations according to a plurality of different communicationprotocols and/or with WLANs in which a plurality of client stationsoperate according to a plurality of different communication protocols.Continuing with the example above, a communication device configured tooperate according to both the UHT communication protocol and a legacycommunication protocol is able to determine that the data unit isformatted according to the UHT communication protocol and not the legacycommunication protocol. Similarly, a communication device configured tooperate according to a legacy communication protocol but not the UHTcommunication protocol is able to determine that the data unit is notformatted according to the legacy communication protocol and/ordetermine a duration of the data unit.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) processing unit 18 and a physicallayer (PHY) processing unit 20. The PHY processing unit 20 includes aplurality of transceivers 21, and the transceivers 21 are coupled to aplurality of antennas 24. Although three transceivers 21 and threeantennas 24 are illustrated in FIG. 1, the AP 14 includes other suitablenumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 inother embodiments. In one embodiment, the MAC processing unit 18 and thePHY processing unit 20 are configured to operate according to a firstcommunication protocol (e.g., UHT communication protocol). In anotherembodiment, the MAC processing unit 18 and the PHY processing unit 20are also configured to operate according to a second communicationprotocol (e.g., IEEE 802.11ac Standard). In yet another embodiment, theMAC processing unit 18 and the PHY processing unit 20 are additionallyconfigured to operate according to the second communication protocol, athird communication protocol and/or a fourth communication protocol(e.g., the IEEE 802.11a Standard and/or the IEEE 802.11n Standard).

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 includes othersuitable numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. At least one of the client stations25 (e.g., client station 25-1) is configured to operate at leastaccording to the first communication protocol. In some embodiments, atleast one of the client stations 25 is not configured to operateaccording to the first communication protocol but is configured tooperate according to at least one of the second communication protocol,the third communication protocol and/or the fourth communicationprotocol (referred to herein as a “legacy client station”).

The client station 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC processingunit 28 and a PHY processing unit 29. The PHY processing unit 29includes a plurality of transceivers 30, and the transceivers 30 arecoupled to a plurality of antennas 34. Although three transceivers 30and three antennas 34 are illustrated in FIG. 1, the client station 25-1includes other suitable numbers (e.g., 1, 2, 4, 5, etc.) of transceivers30 and antennas 34 in other embodiments.

According to an embodiment, the client station 25-4 is a legacy clientstation, i.e., the client station 25-4 is not enabled to receive andfully decode a data unit that is transmitted by the AP 14 or anotherclient station 25 according to the first communication protocol.Similarly, according to an embodiment, the legacy client station 25-4 isnot enabled to transmit data units according to the first communicationprotocol. On the other hand, the legacy client station 25-4 is enabledto receive and fully decode and transmit data units according to thesecond communication protocol, the third communication protocol and/orthe fourth communication protocol.

In an embodiment, one or both of the client stations 25-2 and 25-3, hasa structure the same as or similar to the client station 25-1. In anembodiment, the client station 25-4, has a structure similar to theclient station 25-1. In these embodiments, the client stations 25structured the same as or similar to the client station 25-1 have thesame or a different number of transceivers and antennas. For example,the client station 25-2 has only two transceivers and two antennas,according to an embodiment.

In various embodiments, the PHY processing unit 20 of the AP 14 isconfigured to generate data units conforming to the first communicationprotocol and having formats described hereinafter. The transceiver(s) 21is/are configured to transmit the generated data units via theantenna(s) 24. Similarly, the transceiver(s) 24 is/are configured toreceive the data units via the antenna(s) 24. The PHY processing unit 20of the AP 14 is configured to process received data units conforming tothe first communication protocol and having formats describedhereinafter and to determine that such data units conform to the firstcommunication protocol, according to various embodiments.

In various embodiments, the PHY processing unit 29 of the client device25-1 is configured to generate data units conforming to the firstcommunication protocol and having formats described hereinafter. Thetransceiver(s) 30 is/are configured to transmit the generated data unitsvia the antenna(s) 34. Similarly, the transceiver(s) 30 is/areconfigured to receive data units via the antenna(s) 34. The PHYprocessing unit 29 of the client device 25-1 is configured to processreceived data units conforming to the first communication protocol andhaving formats described hereinafter and to determine that such dataunits conform to the first communication protocol, according to variousembodiments.

FIG. 2A is a diagram of a prior art OFDM data unit 200 that the AP 14 isconfigured to transmit to the client station 25-4 via orthogonalfrequency division multiplexing (OFDM) modulation, according to anembodiment. In an embodiment, the client station 25-4 is also configuredto transmit the data unit 200 to the AP 14. The data unit 200 conformsto the IEEE 802.11a Standard and occupies a 20 Megahertz (MHz) band. Thedata unit 200 includes a preamble having a legacy short training field(L-STF) 202, generally used for packet detection, initialsynchronization, and automatic gain control, etc., and a legacy longtraining field (L-LTF) 204, generally used for channel estimation andfine synchronization. The data unit 200 also includes a legacy signalfield (L-SIG) 206, used to carry certain physical layer (PHY) parametersof with the data unit 200, such as modulation type and coding rate usedto transmit the data unit, for example. The data unit 200 also includesa data portion 208. FIG. 2B is a diagram of example data portion 208(not low density parity check encoded), which includes a service field,a scrambled physical layer service data unit (PSDU), tail bits, andpadding bits, if needed. The data unit 200 is designed for transmissionover one spatial or space-time stream in a single input single output(SISO) channel configuration.

FIG. 3 is a diagram of a prior art OFDM data unit 300 that the AP 14 isconfigured to transmit to the client station 25-4 via orthogonalfrequency domain multiplexing (OFDM) modulation, according to anembodiment. In an embodiment, the client station 25-4 is also configuredto transmit the data unit 300 to the AP 14. The data unit 300 conformsto the IEEE 802.11n Standard, occupies a 20 MHz band, and is designedfor mixed mode situations, i.e., when the WLAN includes one or moreclient stations that conform to the IEEE 802.11a Standard but not theIEEE 802.11n Standard. The data unit 300 includes a preamble having anL-STF 302, an L-LTF 304, an L-SIG 306, a high throughput signal field(HT-SIG) 308, a high throughput short training field (HT-STF) 310, and Mdata high throughput long training fields (HT-LTFs) 312, where M is aninteger generally determined by the number of spatial streams used totransmit the data unit 300 in a multiple input multiple output (MIMO)channel configuration. In particular, according to the IEEE 802.11nStandard, the data unit 300 includes two HT-LTFs 312 if the data unit300 is transmitted using two spatial streams, and four HT-LTFs 312 isthe data unit 300 is transmitted using three or four spatial streams. Anindication of the particular number of spatial streams being utilized isincluded in the HT-SIG field 308. The data unit 300 also includes a dataportion 314.

FIG. 4 is a diagram of a prior art OFDM data unit 400 that the AP 14 isconfigured to transmit to the client station 25-4 via orthogonalfrequency domain multiplexing (OFDM) modulation, according to anembodiment. In an embodiment, the client station 25-4 is also configuredto transmit the data unit 400 to the AP 14. The data unit 400 conformsto the IEEE 802.11n Standard, occupies a 20 MHz band, and is designedfor “Greenfield” situations, i.e., when the WLAN does not include anyclient stations that conform to the IEEE 802.11a Standard but not theIEEE 802.11n Standard. The data unit 400 includes a preamble having ahigh throughput Greenfield short training field (HT-GF-STF) 402, a firsthigh throughput long training field (HT-LTF1) 404, a HT-SIG 406, and Mdata HT-LTFs 408, where M is an integer which generally corresponds to anumber of spatial streams used to transmit the data unit 400 in amultiple input multiple output (MIMO) channel configuration. The dataunit 400 also includes a data portion 410.

FIG. 5 is a diagram of a prior art OFDM data unit 500 that the clientstation AP 14 is configured to transmit to the client station 25-4 viaorthogonal frequency domain multiplexing (OFDM) modulation, according toan embodiment. In an embodiment, the client station 25-4 is alsoconfigured to transmit the data unit 500 to the AP 14. The data unit 500conforms to the IEEE 802.11ac Standard and is designed for “Mixed field”situations. The data unit 500 occupies a 20 MHz bandwidth. In otherembodiments or scenarios, a data unit similar to the data unit 500occupies a different bandwidth, such as a 40 MHz, an 80 MHz, or a 160MHz bandwidth. The data unit 500 includes a preamble having an L-STF502, an L-LTF 504, an L-SIG 506, two first very high throughput signalfields (VHT-SIGAs) 508 including a first very high throughput signalfield (VHT-SIGA1) 508-1 and a second very high throughput signal field(VHT-SIGA2) 508-2, a very high throughput short training field (VHT-STF)510, M very high throughput long training fields (VHT-LTFs) 512, where Mis an integer, and a second very high throughput signal field(VHT-SIG-B) 514. The data unit 500 also includes a data portion 516.

FIG. 6A is a set of diagrams illustrating modulation of the L-SIG,HT-SIG1, and HT-SIG2 fields of the data unit 300 of FIG. 3, as definedby the IEEE 802.11n Standard. The L-SIG field is modulated according tobinary phase shift keying (BPSK), whereas the HT-SIG1 and HT-SIG2 fieldsare modulated according to BPSK, but on the quadrature axis (Q-BPSK). Inother words, the modulation of the HT-SIG1 and HT-SIG2 fields is rotatedby 90 degrees as compared to the modulation of the L-SIG field.

FIG. 6B is a set of diagrams illustrating modulation of the L-SIG,VHT-SIGA1, and VHT-SIGA2 fields of the data unit 500 of FIG. 5, asdefined by the IEEE 802.11ac Standard. Unlike the HT-SIG1 field in FIG.6A, the VHT-SIGA1 field is modulated according to BPSK, same as themodulation of the L-SIG field. On the other hand, the VHT-SIGA2 field isrotated by 90 degrees as compared to the modulation of the L-SIG field.

FIG. 7A is a diagram of an OFDM data unit 700 that the client station AP14 is configured to transmit to the client station 25-1 via orthogonalfrequency domain multiplexing (OFDM) modulation, according to anembodiment. In an embodiment, the client station 25-1 is also configuredto transmit the data unit 700 to the AP 14. The data unit 700 conformsto the first communication protocol and occupies a 20 MHz bandwidth.Data units similar to the data unit 700 occupy other suitable bandwidthsuch as 40 MHz, 80 MHz, 160 MHz, 320 MHz, 640 MHz, for example, or othersuitable bandwidths, in other embodiments. The data unit 700 is suitablefor “mixed mode” situations, i.e. when the WLAN 10 includes a clientstation (e.g., the legacy client station 24-4) that conforms to a legacycommunication protocol, but not the first communication protocol. Thedata unit 700 is utilized in other situations as well, in someembodiments.

The data unit 700 includes a preamble having an L-STF 702, an L-LTF 704,an L-SIG 706, two first ultra high throughput signal fields (UHT-SIGAs)708 including a first ultra high throughput signal field (UHT-SIGA1)708-1 and a second ultra high throughput signal field (UHT-SIGA2) 708-2,an ultra high throughput short training field (UHT-STF) 710, M ultrahigh throughput long training fields (UHT-LTFs) 712, where M is aninteger, and a third ultra high throughput signal field (UHT-SIGB) 714.In an embodiment, the UHT-SIGAs 708 comprise two OFDM symbols, where theUHT-SIGA1 708-1 field comprises the first OFDM symbol and the UHT-SIGA2comprises the second OFDM symbol. In at least some examples, theUHT-SIGAs 708 are collectively referred to as a single very highthroughput signal field (UHT-SIGA) 708. In some embodiments, the dataunit 700 also includes a data portion 716. In other embodiments, thedata unit 700 omits the data portion 716.

In the embodiment of FIG. 7A, the data unit 700 includes one of each ofthe L-STF 702, the L-LTF 704, the L-SIG 706, the UHT-SIGA1s 708. Inother embodiments in which an OFDM data unit similar to the data unit700 occupies a cumulative bandwidth other than 20 MHz, each of the L-STF702, the L-LTF 704, the L-SIG 706, the UHT-SIGA1s 708 is repeated over acorresponding number of 20 MHz sub-bands of the whole bandwidth of thedata unit, in an embodiment. For example, in an embodiment, the OFDMdata unit occupies an 80 MHz bandwidth and, accordingly, includes fourof each of the L-STF 702, the L-LTF 704, the L-SIG 706, the UHT-SIGA1s708, in an embodiment. In some embodiments, the modulation of different20 MHz sub-bands signals is rotated by different angles. For example, inone embodiment, a first subband is rotated 0-degrees, a second subbandis rotated 90-degrees, a third sub-band is rotated 180-degrees, and afourth sub-band is rotated 270-degrees. In other embodiments, differentsuitable rotations are utilized. The different phases of the 20 MHzsub-band signals result in reduced peak to average power ratio (PAPR) ofOFDM symbols in the data unit 700, in at least some embodiments. In anembodiment, if the data unit that conforms to the first communicationprotocol is an OFDM data unit that occupies a cumulative bandwidth suchas 20 MHz, 40 MHz, 80 MHz, 160 MHz, 320 MHz, 640 MHz, etc., the UHT-STF,the UHT-LTFs, the UHT-SIGB and the UHT data portion occupy thecorresponding whole bandwidth of the data unit.

FIG. 7B is a set of diagrams illustrating modulation of the L-SIG 706,UHT-SIGA1 708-1, and UHT-SIGA2 708-2 of the data unit 700 of FIG. 7A,according to an embodiment. In this embodiment, the L-SIG 706, UHT-SIGA1708-1, and UHT-SIGA2 708-2 fields have the same modulation as themodulation of the corresponding field as defined in the IEEE 802.11acStandard and depicted in FIG. 6B. Accordingly, the UHT-SIGA1 field ismodulated the same as the L-SIG field. On the other hand, the UHT-SIGA2field is rotated by 90 degrees as compared to the modulation of theL-SIG field.

In an embodiment, because the modulations of the L-SIG 706, UHT-SIGA1708-1, and UHT-SIGA2 708-2 fields of the data unit 700 correspond to themodulations of the corresponding fields in a data unit that conforms tothe IEEE 802.11ac Standard (e.g., the data unit 500 of FIG. 5), legacyclient stations configured to operate according to the IEEE 802.11aStandard and/or the IEEE 802.11n Standard will assume, in at least somecircumstances, that the data unit 700 conforms to the IEEE 802.11acStandard and will process the data unit 700 accordingly. For example, aclient station the conforms to the IEEE 802.11a Standard will recognizethe legacy IEEE 802.11a Standard portion of the preamble of the dataunit 700 and will set the data unit duration according to a durationindicated in the L-SIG 706. For example, the legacy client station willcalculate a duration based on a rate and a length (e.g., in number ofbytes) indicated in the L-SIG field 706, according to an embodiment. Inan embodiment, the rate and the length in the L-SIG field 706 are setsuch that a client station configured to operate according to a legacycommunication protocol will calculate, based the rate and the length, apacket duration (T) that corresponds to, or at least approximates, theactual duration of the data unit 700. For example, the rate is set toindicate a lowest rate defined by the IEEE 802.11a Standard (i.e., 6Mbps), and the length is set to a value computed such that packetduration computed using the lowest rate at least approximates the actualduration of the data unit 700, in one embodiment.

In an embodiment, a legacy client station that conforms to the IEEE802.11a Standard, when receiving the data unit 700, will compute apacket duration for the data unit 700, e.g., using a rate and a lengthfields of L-SIG field 706, and will wait until the end of the computedpacket duration before performing clear channel assessment (CCA), in anembodiment. Thus, in this embodiment, communication medium is protectedagainst access by the legacy client station at least for the duration ofthe data unit 700. In an embodiment, the legacy client station willcontinue decoding the data unit 700, but will fail an error check (e.g.,using a frame check sequence (FCS)) at the end of the data unit 700.

Similarly, a legacy client station configured to operate according tothe IEEE 802.11n Standard, when receiving the data unit 700, willcompute a packet duration (T) of the data unit 700 based on the rate andthe length indicated in the L-SIG 706 of the data unit 700, in anembodiment. The legacy client station will detect the modulation of thefirst UHT signal field (UHT-SIGA1) 708-1 (BPSK) and will assume that thedata unit 700 is a legacy data unit that conforms to the IEEE 802.11aStandard. In an embodiment, the legacy client station will continuedecoding the data unit 700, but will fail an error check (e.g., using aframe check sequence (FCS)) at the end of the data unit. In any event,according to the IEEE 802.11n Standard, the legacy client station willwait until the end of a computed packet duration (T) before performingclear channel assessment (CCA), in an embodiment. Thus, communicationmedium will be protected from access by the legacy client station forthe duration of the data unit 700, in an embedment.

A legacy client station configured to operate according to the IEEE802.11ac Standard but not the first communication protocol, whenreceiving the data unit 700, will compute a packet duration (T) of thedata unit 700 based on the rate and the length indicated in the L-SIG706 of the data unit 700, in an embodiment. However, the legacy clientstation will not be able to detect, based on the modulation of the dataunit 700, that the data unit 700 does not conform to the IEEE 802.11acStandard, in an embodiment. In some embodiments, one or more UHT signalfields (e.g., the UHT-SIGA1 and/or the UHT-SIGA2) of the data unit 700is/are formatted to intentionally cause the legacy client station todetect an error when decoding the data unit 700, and to therefore stopdecoding (or “drop”) the data unit 700. For example, UHT-SIGA 708 of thedata unit 700 is formatted to intentionally cause an error when the SIGAfield is decoded by a legacy device according to the IEEE 802.11acStandard, in an embodiment. Further, according to the IEEE 802.11acStandard, when an error is detected in decoding the VHT-SIGA field, theclient station will drop the data unit 700 and will wait until the endof a computed packet duration (T), calculated, for example, based on arate and a length indicated in the L-SIG 706 of the data unit 700,before performing clear channel assessment (CCA), in an embodiment.Thus, communication medium will be protected from access by the legacyclient station for the duration of the data unit 700, in an embedment.

FIGS. 8A-8G are diagrams of example bit allocations for various portionsof the UHT-SIGA field 708, according to an embodiment. In particular,FIGS. 8A-8C are diagrams of example bit allocations for the UHT-SIGA1field 708-1 (or portions of the UHT-SIGA1 field 708-1), and FIGS. 8D-8Gare diagrams of example bit allocations for the UHT-SIGA2 field 708-2(or portions of the UHT-SIGA1 field 708-2), according to an embodiment.The UHT-SIGA field 708 is generally formatted similar to a VHT-SIGA1field as specified in the IEEE 802.11ac Standard, but one or moresubfields of the UHT-SIGA field 708 are altered as compared to thecorresponding subfields defined in the IEEE 802.11ac Standard and/orinclude values unsupported by the IEEE 802.11ac Standard tointentionally cause a legacy client station configured to operateaccording to the IEEE 802.11ac Standard to detect an error from theUHT-SIGA field 708, in some embodiments.

Referring to FIG. 8A, the UHT-SIGA1 field 708-1 includes a plurality ofsubfield 802 that collectively comprise 24 information bits, in theillustrated embodiment. The plurality of subfields 802 includes a 2-bitbandwidth (BW) subfield 802-1, a first 1-bit reserved subfield 802-2, a1-bit space time block coding (STBC) subfield 802-3, a 6-bit GroupIdentification (Group ID) subfield 802-4, a 12-bit NSTS/Partial AIDsubfield 802-5, the content of which depends on whether the data unit700 is a single user data unit (e.g., a data unit that used to transmitinformation to a single client station) or in a multiuser data unit(e.g., a data unit that includes independent data streams to multipleclient stations), a 1-bit TXOP_PS_NOT_ALLOWED subfield 802-6, and asecond 1-bit reserved subfield 802-7. FIGS. 8B and 8C are diagrams ofthe NSTS/Partial AID subfield 802-5 for a single user and a multi userdata unit, respectively, according to an embodiment. Referring to FIG.8B, in an embodiment in which the data unit 700 is a single user dataunit, the NSTS/Partial AID subfield 802-5 comprises a 3-bit single usernumber of space-time streams subfield 802-5 a and a 9-bit Partial AIDsubfield 802-5 b. Referring to FIG. 8C, in an embodiment in which thedata unit 700 is a multiuser data unit, the NSTS/Partial AID subfield802-5 comprises four 3-bit user Nsts subfields 802-5 c through 802-5 f,where each of the user subfields 802-5 c through 802-5 f indicates anumber of space time streams corresponding to a intended recipient ofthe signal field 800.

Referring to now FIG. 8D, the UHT-SIGA2 field 708-2 includes a pluralityof subfield 810 that collectively comprise 24 information bits, in theillustrated embodiment. The plurality of subfields 810 includes a 1-bitShort GI subfield 810-1, a 1-bit Short GI NSYM Disambiguation subfield810-2, a 1-bit SU/MU[0] Coding subfield 910-3, a 1-bit LDPC Extra OFDMSymbol subfield 810-4, a 12-bit SU MCS/MU[1-3] Coding subfield 910-5,the content of which depends on whether the data unit 700 is a singleuser data unit or a multiuser data unit, a 1-bit beamsteering/reservedsubfield 810-6, a reserved subfield 810-7, an 8-bit cyclic redundancycheck (CRC) subfield 810-8, and a tail subfield 810-9. FIGS. 8E and 8Fare diagrams of the SU MCS/MU[1-3] Coding subfield 810-5 for a singleuser and a multi user data unit, respectively. Referring to FIG. 8E, inan embodiment in which the data unit 700 is a single user data unit, theSU MCS/MU[1-3] Coding subfield 810-5 comprises a 4-bit single SU MCSsubfield 810-5 a. Referring to FIG. 8F, in an embodiment in which thedata unit 700 is a multiuser data unit, the SU MCS/MU[1-3] Codingsubfield 810-5 comprises four 1-bit subfields 810-5 b through 810-5 e,where each of the subfields 810-5 b through 810-5 d indicates a codingutilized for a particular intended recipient of the signal field 810,and the subfield 810-5 e is reserved.

In some embodiments, a signal field of a data unit that conforms to thefirst communication protocol (e.g., the UHT-SIGA field 708 of the dataunit 700) is formatted similarly to a corresponding signal field of alegacy data unit specified by a legacy communication protocol (e.g., theVHT-SIGA as specified in the IEEE 802.11ac Standard), but with a set ofone or more information bits generated differently than thecorresponding information bits generated according to the legacycommunication protocol. For example, the set of one or more informationbits includes information bits generated an error detection scheme(e.g., CRC) not specified by the legacy communication protocol, in anembodiment. As another example, the set of one or more information bitsincludes information bits set to indicate a mode not supported by thelegacy communication protocol, in an embodiment. The differences betweenthe signal field formatted according to the first communication protocoland a signal field formatted according to the legacy communicationprotocol cause a receiving device that conforms to the secondcommunication protocol, but not the first communication protocol, todetect an error when decoding a signal field of a data unit thatconforms to the first communication protocol, in at least someembodiments and/or scenarios. Further, such differences permit areceiver device that conforms to the first communication protocolwhether a data unit being received conforms to the first communicationprotocol or to a legacy communication protocol, in at least someembodiments.

For example, in some embodiments, CRC to be included in the CRC subfield810-8 (FIG. 8C) is generated differently than CRC specified for theVHT-SIGA field by the IEEE 802.11ac Standard. The different CRC for theUHT-SIGA 708 field will cause a CRC error when the UHT-SIGA field 708 isdecoded by a client station that conforms to the IEEE 802.11ac Standard,but not the first communication protocol, in an embodiment. Further, thedifferent CRC will permit a client station that conforms to the firstcommunication protocol to determine that the data unit 700 conforms tothe first communication protocol, in an embodiment.

FIGS. 9A-9C are diagrams depicting several example CRC generationschemes 950, 960, 970 used for generating CRC for a UHT-SIGA field of adata unit that conforms to the first communication protocol, accordingto some embodiments. In various embodiments, the CRC generation schemes950, 960, 970 are used to generate the CRC subfield 810-8 (FIG. 8D) or aCRC field for another suitable UHT-SIGA field of a data unit thatconforms to the first communication protocol.

Referring to FIG. 9A, according to the CRC generation scheme 950, an8-bit CRC for the UHT-SIGA field is generated using a polynomial that isdifferent from the polynomial specified for the VHT-SIGA field in theIEEE 802.11ac Standard, in an embodiment. For example, an 8-bitpolynomial at least substantially orthogonal to the polynomial specifiedfor the VHT-SIGA field is utilized at block 952, in one embodiment. Inother embodiments, other suitable polynomials different from the CRCpolynomial specified for the VHT-SIGA field are utilized at block 952.Referring now to FIG. 9B, according to the CRC generation scheme 960, an8-bit CRC for the UHT-SIGA 708 is generated using the polynomialspecified for the VHT-SIGA field in the IEEE 802.11ac Standard (block962), but one or more bits of the generated CRC are flipped (i.e., “0”changed to “1” and “1” changed to “0”), or otherwise encrypted (block964), in this embodiment.

Referring now to FIG. 9C, according to the CRC generation scheme 970, aCRC having less bits than the 8-bit CRC specified for the VHT-SIGA fieldin the IEEE 802.11ac Standard is generated for the UHT-SIGA field, in anembodiment. For example, a 4-bits CRC is generated for the UHT-SIGA, insome embodiments. The 4-bit CRC is generated, for example, using thepolynomial specified for the VHT-SIGA field in the IEEE 802.11acStandard (block 972). Then, a 4-bit subset of the generated CRC (block974) is selected. For example, the four most significant bits (MSB) orthe four most significant bits (LSB) of the generated CRC (block 974)are selected, in some embodiments, Further, one or more bits of theselected 4-bit CRC are flipped (i.e., “0” changed to “1” and “1” changedto “0”), or otherwise encrypted (block 976), in this embodiment. Inother embodiments, the CRC generation scheme 970 generates a CRC that isanother suitable number of bits less than 8 (e.g., 7 bits, 6 bits, 5bits, etc.). For example, a 5-bit CRC is generated using the polynomialspecified for the VHT-SIGA field in the IEEE 802.11ac Standard,selecting five most significant bits (MSB) of the generated CRC, thefive least significant bits (LSB) of the generated CRC, or another 5-bitsubset of the generated CRC, and encrypting (e.g., flipping) one or morebits of the resulting 5-bit CRC, in some embodiments. In someembodiments in which fewer CRC bits are utilized (e.g., fewer than 8),the remaining bit locations of the UHT-SIGA field (e.g., the other onesof MSBs or LSBs of the CRC subfield 810-8 of FIG. 8D) are reservedand/or are utilized to signal additional information relevant to thefirst communication protocol.

While FIGS. 9A-9C depict several example CRC generation schemes utilizedfor the UHT-SIGA field 708 according to some embodiments, in general,any CRC generation scheme different than a CRC generation schemespecified for the VHT-SIGA field by the IEEE 802.11ac Standard can beutilized, and other suitable CRC generation are utilized to generate CRCfor the UHT-SIGA field 708 in other embodiments.

As just an example, in some embodiments, CRC having less bits than the8-bit CRC specified for the VHT-SIGA field in the IEEE 802.11ac Standardis generated for the UHT-SIGA field using a polynomial that is differentfrom the polynomial specified by the IEEE 802.11ac Standard. Forexample, an x-bit CRC is generated using an x-bit polynomial designedsuch that the generated CRC is at least substantially uncorrelated withthe corresponding bits of the VHT-SIGA CRC generated according to theIEEE 802.11ac Standard, where x is an integer between 1 and 7, in someembodiments. In some such embodiments, the remaining bit locations ofthe UHT-SIGA field that correspond to bit locations of the CRC subfieldof a VHT-SIGA field defined by the IEEE 802.11ac Standard (e.g., theother ones of MSBs or LSBs of the CRC subfield 910-8 of FIG. 8D) arereserved or are utilized to signal additional information relevant tothe first communication protocol.

In an embodiment, differences in CRC generation for the UHT-SIGA fieldaccording to the first communication protocol and for the VHT-SIGA fieldas defined in the IEEE 802.11ac Standard will cause a legacy clientstation configured to operate according to the IEEE 802.11ac Standard todetect a CRC error when decoding the data unit 700 and to therefore dropthe data unit 700. Further, differences in CRC generation for theUHT-SIGA field according to the first communication protocol and for theVHT-SIGA field defined in the IEEE 802.11ac Standard will permit aclient station configured to operate according to the firstcommunication protocol, when receiving a data unit, to detect whetherthe data unit conforms to the first communication protocol or to theIEEE 802.11ac Standard.

FIG. 10 is a block diagram depicting a detection scheme 1000 used by aclient station (e.g., the client station 25-1) configured to operateaccording the first communication protocol to determine whether a dataunit conforms to the first communication protocol or to a legacycommunication protocol (e.g., the IEEE 802.11ac Standard), according toan embodiment. The detection scheme 1000 is suitable for use inembodiments in which the UHT-SIGA field of data units conforming to thefirst communication protocol include a CRC having the same number ofbits as CRC specified for a corresponding field by the legacycommunication protocol (e.g., 8 bits). According to the detection scheme1100, a client station receiving a data unit decodes the SIGA field ofthe data unit. After decoding the signal field, the client stationexcludes CRC bits and BCC tail bits from the decoded SIGA field togenerate a set of bits based on which a CRC for the SIGA field of thedata unit should be generated, in an embedment. Then, a first CRC forthe SIGA field is generated (bock 1002) based on the set of bits andusing a CRC generation scheme specified in the first communicationprotocol. A second CRC for the SIGA field is generated (bock 1004) basedon the set of bits and using a CRC generation scheme specified in thelegacy communication protocol (e.g., the IEEE 802.11ac Standard). Thefirst generated CRC and the second generated CRC is each compared (bock1006) to the received CRC that was received in the SIGA field of thedata unit. When a match is detected between the received CRC and thefirst generated CRC, it is determined that the data unit conforms to thefirst communication protocol, in an embodiment. On the other hand, whena match is detected between the received CRC and the second generatedCRC, it is determined that the data unit conforms to the legacycommunication protocol (e.g., the IEEE 802.11ac Standard), in anembodiment.

FIG. 11 is a block diagram depicting a detection scheme 1100 used by aclient station (e.g., the client station 25-1) configured to operateaccording the first communication protocol to detect to whether a dataunit conforms to the first communication protocol or to a legacycommunication protocol, according to another embodiment. The detectionscheme 1100 is suitable for use in embodiments in which the UHT-SIGAfield of data units conforming to the first communication protocolinclude fewer bits (e.g., 4 bits) than the number of CRC bits specifiedfor a corresponding field by the legacy communication protocol,according to an embodiment. According to the detection scheme 1100, theclient station, when receiving a data unit, decodes the SIGA field ofthe data unit. The client station then excludes CRC bits and BCC tailbits from the decoded SIGA field to generate a set of bits based onwhich CRC for the SIGA field should be generated. Then, a first CRC forthe received SIGA field is generated (bock 1102) based on the set ofbits and using the CRC generation scheme specified in the firstcommunication protocol. In the embodiment of FIG. 11, CRC according tothe field communication protocol is generated using a CRC polynomialspecified for the corresponding field by the legacy communicationprotocol, selecting a subset of bits of the generated CRC (e.g., fourLSBs, four MSBs, another suitable subset of CRC bits, etc.) to beutilized for the first CRC, and encrypting one or more bits in theselected subset to generate the first CRC. A second CRC for the SIGAfield is generated (bock 1104) based on the set of bits and according tothe CRC generation scheme specified in the IEEE 802.11ac Standard andusing four LSB or four MSB of the generated CRC as the second CRC. Thefirst generated CRC and the second generated CRC are compared (bock1106) to the corresponding bits of the CRC that was received in the SIGAfield of the data unit. When a match is detected between the receivedCRC and the first generated CRC, it is determined that the data unitconforms to the first communication protocol, in an embodiment. On theother hand, when a match is detected between the received CRC and thesecond generated CRC, it is determined that the data unit conforms tothe legacy communication protocol (e.g., the IEEE 802.11ac Standard), inan embodiment.

In some embodiments, in addition to or instead of using CRC tointentionally cause a legacy station to detect an error from theUHT-SIGA field 708, one or more subfields of the UHT-SIGA field 708 areset to indicate a mode that is not supported by legacy client stationsconfigured to operate according to the legacy communication protocol tointentionally cause a legacy station to detect an error from theUHT-SIGA field 708. For example, the UHT-SIGA field 708 includes anindication of a modulation and coding scheme not supported by a legacyclient station operating according to the IEEE 802.11ac Standard tointentionally cause the legacy client station to detect an error whendecoding the UHT-SIGA field 708, and an embodiment. As another example,in some embodiments, the UHT-SIGA field 708 includes subfieldcombination that is not supported or “unallowable” according to the IEEE802.11ac Standard. For example, for a single user data unit, the GroupID subfield of the UHT-SIGA field 708 is set to a value of 0 or 63 andthe SU MCS field 902-5 b is set to indicate an MCS greater than 9, in anembodiment. As another example, in another embodiment, the STBC subfield902-3 and the SU NSTS subfield 902-5 a are both set to a logic one (1).As yet another example, in yet another embodiment, for a multi-user dataunit, the STBC subfield 902-3 and each of Nsts subfields 902-5 c through902-5 f is set to a logic one (1). In other embodiments, other SIGAsubfield combinations unallowable in the IEEE 802.11ac Standard areutilized in the UHT-SIGA field 708 to intentionally cause an error whenthe UHT-SIG field 708 is decoded by a legacy client station. Further,such unallowable combinations included in the UHT-SIGA field 708 of thedata unit 700 indicate to a client station that conforms to the firstcommunication protocol that the data unit 700 conforms to the firstcommunication protocol, in some embodiments.

In some embodiments, one or more additional indications is/are includedin the UHT-SIGA field 708 of the data unit 700 to indicate to a clientstation configured to operate according to the first communicationprotocol that the data unit 700 conforms to the first communicationprotocol. For example, a subfield that corresponds to a reservedsubfield in a VHT-SIGA field generated according to the IEEE 802.11acStandard is set to a logic zero (0) in the UHT-SIGA field 708 toindicate to a client station configured to operate according to thefirst communication protocol that the data unit 700 conforms to thefirst communication protocol. In this embodiment, a client stationoperating according to the first communication protocol, when receivinga data unit, determines that the data unit conforms to the firstcommunication protocol if the reserved bit in the UHT-SIGA field is setof logic zero (0) and determines that the data unit conforms to the IEEE802.11ac Standard if the reserved bit is set to a logic one (1), in anembodiment.

In some embodiments, at least some portions (e.g., subfields) of aUHT-SIGA field (e.g., the UHT-SIGA field 708) that are not used tointentionally cause an error at a legacy device are not formatted thesame as the corresponding portions (e.g., subfields) of a VHT-SIGA fieldspecified by the IEEE 802.11ac Standard. For example, such portions arealtered to include additional information relevant to the firstcommunication protocol, in some embodiments. For example, whereas theVHT-SIGA field specified by the IEEE 802.11ac Standard includes two bitsto indicate the BW of a data unit, some data units that conform, to thefirst communication protocol occupy wider bandwidth than the widestbandwidth specified by the IEEE 802.11ac Standard. Thus, in someembodiments, one or more extra bits are needed to signal the bandwidthfor data units that conform to the first communication protocol. Forexample, in one embodiment, the UHT-SIGA field includes a 3-bitbandwidth indication. Additionally or alternatively, in someembodiments, extra signal field bits are utilized for the UHT-SIGA fieldto signal new physical layer (PHY) features that are not present in theIEEE 802.11ac Standard.

In some such embodiments, VHT-SIGA subfields that are reserved accordingto the IEEE 802.11ac Standard are utilized in the UHT-SIGA field tosignal the wider bandwidth and/or additional PHY features according tothe first communication protocol. Additionally or alternatively, in someembodiments in which UHT-SIGA utilizes a shorter than the eight bit CRCdefined for VHT-SIGA in the IEEE 802.11ac Standard, bits correspondingto the remaining CRC bits of the VHT-SIGA field are utilized in theUHT-SIGA field to signal the wider bandwidth and/or additional PHYfeatures according to the first communication protocol.

In some embodiments in which the UHT-SIGA field 708 includes an explicitindication to signal that the data unit 700 conforms to the firstcommunication protocol, schemes designed to intentionally cause an errorat a legacy client station are not employed for the UHT-SIGA field 708.For example, in an embodiment, CRC for the UHT-SIGA field 708 isgenerated using the VHT-SIGA CRC polynomial specified in the IEEE802.11ac Standard and with the same number of bits as specified in theIEEE 802.11ac Standard. Further, in this embodiment, a subfield thatcorresponds to a reserved subfield in a VHT-SIGA field generatedaccording to the IEEE 802.11ac Standard is set to a logic zero (0) inthe UHT-SIGA field 708 to indicate to a client station configured tooperate according to the first communication protocol that the data unit700 conforms to the first communication protocol. In this case, a clientstation configured to operate according to the first communicationprotocol will determine that the data unit 700 conforms to the firstcommunication protocol based on the indication included in the UHT-SIGAfield 708. However, a legacy client station client station receiving thedata unit 700, in this case, will not necessary detect an error from theUHT-SIGA field 708 and will not necessarily drop the data unit 700. Insome situations, in such embodiments, the legacy client station willdrop the data unit 700 even without detecting an intentionally causederror from the UHT-SIGA field 708. For example, the legacy clientstation will determine that the partial address identification (PAID)and/or the group ID (GID) included in the UHT-SIGA field 708 do notmatch the corresponding parameters of the client station, and will drop(stop decoding) the data unit 700 based on this determination. In otherembodiments, however, the legacy client station will not drop the dataunit 700 even when the client station determines that the partialaddress identification (PAID) and/or the group ID (GID) included in theUHT-SIGA field 708 do not match the corresponding parameters of theclient station. In this case, the client station will continue decodingthe data unit 700 for the duration of the data unit 700, and willdiscard the data unit 700 based on a failed FCS check at the end of thedata unit 700, in at least some situations.

In another embodiment, CRC for the UHT-SIGA field 708 is generated usingthe VHT-SIGA CRC polynomial specified in the IEEE 802.11ac Standard, butwith fewer bits than specified in the IEEE 802.11ac Standard. Forexample, a CRC is generated using the VHT-SIGA CRC polynomial and xnumber of the generated CRC is/are used as the CRC for the UHT-SIGAfield 708. For example, four (or another suitable number, such as e.g.,5 or 6) MSB or LSB of the CRC generated using the VHT-SIGA CRCpolynomial are utilized, in some embodiments. In some such embodiments,the remaining bit locations of the CRC subfield are reserved or areutilized to signal additional information relevant to the firstcommunication protocol. In such embodiments, although CRC is notintentionally designed to cause an error from the UHT-SIGA field at alegacy client device, it is highly likely that such an error will bedetected, in which case the client station will drop the data unit 700.Further, in such embodiments, a client station configured to operateaccording to the first communication protocol will perform a CRC checkfor the UHT-SIGA field 708 by generating CRC based on received bits ofthe UHT-SIGA field 708 using the CRC polynomial specified for theVHT-SIGA field in the IEEE 802.11ac Standard and comparing 4 (or anothersuitable number, such as e.g., 5 or 6) MSB or LSB of the generated CRCto the received CRC in the UHT-SIGA field. Upon passing the CRC check,the client station will decode the received UHT-SIGA field and willdetermine that the data unit 700 conforms to the first communicationprotocol based on the indication included in the UHT-SIGA field.

FIG. 12 is a diagram of an OFDM data unit 1200 that the client stationAP 14 is configured to transmit to the client station 25-1 viaorthogonal frequency domain multiplexing (OFDM) modulation, according toan embodiment. In an embodiment, the client station 25-1 is alsoconfigured to transmit the data unit 1200 to the AP 14. The data unit1200 conforms to the first communication protocol and occupies a 20 MHzbandwidth. Data units similar to the data unit 1200 occupy othersuitable bandwidth such as 40 MHz, 80 MHz, 160 MHz, 320 MHz, 640 MHz,for example, or other suitable bandwidths, in other embodiments. Thedata unit 1200 is suitable for “mixed mode” situations, i.e. when theWLAN 10 includes a client station (e.g., the legacy client station 24-4)that conforms to a legacy communication protocol, but not the firstcommunication protocol. The data unit 1200 is utilized in othersituations as well, in some embodiments.

The data unit 1200 is similar to the data unit 700 of FIG. 7A, exceptthat the data unit 1200 includes two UHT-SIGB fields 1204 as compared toa single UHT-SIG field 714 included in the data unit 700. Further,UHT-SIGA fields 1202 are different from the UHT-SIGA fields 708 of thedata unit 700, in some embodiments. For example, one or more informationbits of the UHT-SIGA fields 708 are moved from the UHT-SIGA fields 1202to the UHT-SIGB fields 1204, on an embodiment. For example, one or moreinformation bits that are not required for determining appropriateprocessing of the UHT-LTFs 712 are moved to the UHT-SIGB fields 1204, insome embodiments. Various UHT-SIGA generation schemes used tointentionally cause a legacy client station to detect an error from theUHT-SIGA and/or to indicate to a client station configured to operateaccording to the first communication protocol that the data unit 700conforms to the first communication protocol are applied to the UHT-SIGAfields 1202, in at least some embodiments.

FIG. 13A is a diagram of an OFDM data unit 1300 that the client stationAP 14 is configured to transmit to the client station 25-1 viaorthogonal frequency domain multiplexing (OFDM) modulation, according toan embodiment. In an embodiment, the client station 25-1 is alsoconfigured to transmit the data unit 1300 to the AP 14. The data unit1300 conforms to the first communication protocol and occupies a 20 MHzbandwidth. Data units similar to the data unit 1300 occupy othersuitable bandwidth such as 40 MHz, 80 MHz, 160 MHz, 320 MHz, 640 MHz, orother suitable bandwidths, in other embodiments. The data unit 1300 issuitable for “mixed mode” situations, i.e. when the WLAN 10 includes aclient station (e.g., the legacy client station 24-4) that conforms to alegacy communication protocol, but not the first communication protocol.The data unit 1300 is utilized in other situations as well, in someembodiments.

The data unit 1300 is similar to the data unit 700 of FIG. 7A, exceptthat the data unit 1200 includes three UHT-SIGA fields 1302 as comparedto two UHT-SIGA field 708 included in the data unit 700. In someembodiments, data unit similar to the data unit 1300 include othersuitable numbers (e.g., 4, 5, 6, etc.) of the UHT-SIGA fields 1302. EachUHT-SIGA field 1302 comprises one OFDM symbol of the data unit 1300, inan embodiment. Additional UHT-SIGA fields 1320 as compared to the twoUHT-SIGA fields 708 of the data unit 700 are utilized to carryadditional information relevant to the first communication protocol, forexample to signal wider bandwidths defined in the first communicationprotocol, or to signal additional PHY features included in the firstcommunication protocol. In some embodiments, UHT-SIGB field 1308 isomitted from the data unit 1300, and at least some of the Informationincluded in the UHT-SIGB field 1308 (e.g., MU information) is moved tothe UHT-SIGA fields 1302, in some such embodiments.

FIG. 13B is a set of diagrams illustrating modulation of the L-SIG 706,UHT-SIGA1 1302-1, and UHT-SIGA2 1302-2, and UHT-SIGA2 1302-2 of the dataunit 1300 of FIG. 13A, according to an embodiment. In this embodiment,the L-SIG 706, the UHT-SIGA1 1302-1, and the UHT-SIGA2 1302-2 fields aremodulated according to BPSK modulation, signaling to legacy clientstations configured to operate to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard that the data unit 1300 conforms to the IEEE802.11a Standard. Accordingly, legacy client stations configured tooperate to the IEEE 802.11a Standard, the IEEE 802.11n Standard and/orthe IEEE 802.11ac will process the data unit 1300 in the same mannerthat such devices would treat an IEEE 802.11a packet, in at least someembodiments and/or scenarios. For example, a legacy client station willcompute, based on the L-SIG field 706, a packet duration for the dataunit 1300, and will wait until the end of the computed packet durationbefore performing clear channel assessment (CCA), in an embodiment.Further, a client station configured to operate according to the firstcommunication protocol will detect the modulation of the UHT-SIGA3 field1302-3 (e.g., Q-BPSK) and, based on the detected modulation, willdetermined that the data unit 1300 conforms to the first communicationprotocol, in an embodiment.

FIG. 14A is a diagram of an OFDM data unit 1400 that the client stationAP 14 is configured to transmit to the client station 25-1 viaorthogonal frequency domain multiplexing (OFDM) modulation, according toan embodiment. In an embodiment, the client station 25-1 is alsoconfigured to transmit the data unit 1400 to the AP 14. The data unit1400 conforms to the first communication protocol and occupies a 20 MHzbandwidth. Data units similar to the data unit 1400 occupy othersuitable bandwidth such as 40 MHz, 80 MHz, 160 MHz, 320 MHz, 640 MHz, orother suitable bandwidths, in other embodiments. The data unit 1400 issuitable for situations in which the WLAN 10 does not include any clientstations configured to operate to the IEEE 802.11a Standard but not theIEEE 802.11n Standard, in some embodiments.

The data unit 1400 includes a preamble having an ultra high throughputshort training field (UHT-STF) 1402, a first ultra high throughput longtraining field (UHT-LTF) 1404, two legacy high throughput signal fields(HT-SIGs) 1406 including a first high throughput signal field (HT-SIG1)1406-1 and a second high throughput signal field (HT-SIG2) 1406-2, twoultra high throughput signal fields (UHT-SIGs) 1408 including a firstultra high throughput signal field (UHT-SIG1) 1408-1 and a second ultrahigh throughput signal field (UHT-SIG2) 1408-2, M ultra high throughputlong training fields (UHT-LTFs) 1410, where M is an integer, and a thirdultra high throughput signal field (UHT-SIGB) 714. In an embodiment, theUHT-SIGAs 1408 comprise two OFDM symbols, where the UHT-SIGA1 1408-1field comprises the first OFDM symbol and the UHT-SIGA2 1408-2 comprisesthe second OFDM symbol. In at least some examples, the UHT-SIGAs 1408are collectively referred to as a single very high throughput signalfield (UHT-SIGA) 1408. In some embodiments, the data unit 1400 alsoincludes a data portion 1414. In other embodiments, the data unit 1400omits the data portion 1414.

In the embodiment of FIG. 1400A, the data unit 1400 includes one of eachof the UHT-STF 1402, the UHT-LTF1 1403, the HT-SIG 1406 and the UHT-SIGA1408. In other embodiments in which an OFDM data unit similar to thedata unit 1400 occupies a cumulative bandwidth other than 20 MHz, eachof the UHT-STF 1402, the UHT-LTF1 1403, the HT-SIG 1406 and the UHT-SIGA1408 is repeated over a corresponding number of 20 MHz sub-bands of thewhole bandwidth of the data unit, in an embodiment. For example, in anembodiment, the OFDM data unit occupies an 80 MHz bandwidth and,accordingly, includes four of each of the UHT-STF 1402, the UHT-LTF11403, the HT-SIG 1406 and the UHT-SIGA 1408. In some embodiments, themodulation of different 20 MHz sub-bands signals is rotated by differentangles. For example, in one embodiment, a first subband is rotated0-degrees, a second subband is rotated 90-degrees, a third sub-band isrotated 180-degrees, and a fourth sub-band is rotated 270-degrees. Inother embodiments, different suitable rotations are utilized. Thedifferent phases of the 20 MHz sub-band signals result in reduced peakto average power ratio (PAPR) of OFDM symbols in the data unit 700, inat least some embodiments.

Further, if the data unit conforming to the first communication protocolis an OFDM data unit that occupies a cumulative bandwidth such as 20MHz, 40 MHz, 80 MHz, 160 MHz, 320 MHz, 640 MHz, etc., UHT-LTFs 1410, theUHT-SIGB 1412 and the UHT data portion 1414 occupy the correspondingwhole bandwidth of the data unit, according to an embodiment. Further,in an embodiment, each of the UHT-STF 1402, the UHT-LTF1 1403, theHT-SIG 1406 and the UHT-SIGA 1408 are single stream fields mapped tomultiple spatial streams of the data unit 1400 using a column (e.g., thefirst column) or a row (e.g., the first row) of a spatial stream mappingmatrix (“P matrix”) used for mapping multi-stream portion of the dataunit 1400 e.g., the UHT-LTFs 1410, the UHT-SIGB 1412 and the UHT dataportion 1414) to multiple spatial streams.

In some embodiments, data units similar to the data unit 1300 includeother suitable numbers (e.g., 4, 5, 6, etc.) of the UHT-SIGA fields1408. Each UHT-SIGA field 1408 comprises one OFDM symbol, in anembodiment. Additional UHT-SIGA fields 1408 are utilized to carryadditional information relevant to the first communication protocol, forexample to signal wider bandwidths defined in the first communicationprotocol, or to signal additional PHY features included in the firstcommunication protocol, in some embodiments. Further, the UHT-SIGB field1412 is omitted from the data unit 1400, and at least some of theinformation included in the UHT-SIGB field 1412 (e.g., MU information)is moved to the UHT-SIGA fields 1406, in some such embodiments.

FIG. 14B is a set of diagrams illustrating modulation of HT-SIG1 1406-1,UHT-SIGA2 1406-2, and UHT-SIGA1 1408-1 and UHT-SIGA2 1408-2 of the dataunit 1400 of FIG. 14A, according to an embodiment. In the illustratedembodiment, HT-SIG1 1406-1, UHT-SIGA2 1406-2, and UHT-SIGA1 1408-1 aremodulated using Q-BPSK modulation. In an embodiment, legacy clientstations configured to operate to the IEEE 802.11n Standard and/or theIEEE 802.1ac Standard detect Q-BPSK modulation of the HT-SIG1 1406-1,UHT-SIGA2 1406-2, and UHT-SIGA1 1408-1 and, based on the detectedmodulation, will process the data unit 1400 as the legacy client stationwould process an IEEE 802.11n Greenfield packet. In such embodiments,the legacy client station will calculate a duration based on a rate anda length (e.g., in number of bytes) indicated in the HT-SIG field 1406of the data unit 1400. In an embodiment, the rate and the length in theHT-SIG field 1406 are set such that a client station configured tooperate according to a legacy communication protocol will calculate,based the rate and the length, a packet duration (T) that correspondsto, or at least approximates, the actual duration of the data unit 1400.For example, the rate is set to indicate a lowest rate defined by theIEEE 802.11n Standard (i.e., 6 Mbps), and the length is set to a valuecomputed such that packet duration computed using the lowest rate atleast approximates the actual duration of the data unit 1400. A legacyclient station, when receiving the data unit 1400, will compute a packetduration for the data unit 1400, and will wait until the end of thecomputed packet duration before performing clear channel assessment(CCA), in an embodiment. Further, a client station configured to operateaccording to the first communication protocol will detect the modulationof the UHT-SIGA2 field 1408-2 (e.g., Q-BPSK) of the data unit 1400 andwill determine that the data unit 1400 conforms to the firstcommunication protocol, according to an embodiment.

FIG. 15A is a block diagram of an example transmitter 1500 configured togenerate an OFDM symbol, according to an embodiment. For example, in anembodiment, the transmitter 1500 generates an OFDM symbol correspondingto the VHT-SIGA fields 508 of the data unit 500 (FIG. 5). In anotherexample, in an embodiment, the transmitter 1500 generates an OFDM symbolcorresponding to the UHT-SIGA fields 708 of the data unit 700 (FIG. 7A).In various embodiments, the transmitter generates an OFDM symbolcorresponding to other portions of the data unit 500 or the data unit700. Referring to FIG. 1, the AP 14 and the client station 25-1, in oneembodiment, each include a transmitter such as the transmitter 1500 intheir respective network interfaces 16 and 27.

According to an embodiment, the transmitter 1500 includes an encoder1502. The encoder 1502 receives one or more blocks 1504 of data, each ofwhich includes bits from one or more UHT-SIGA fields (such as theUHT-SIGA1 and UHT-SIGA2 fields shown in FIG. 7, FIG. 12, FIG. 13, andFIG. 14A). In an embodiment, the contents of a given UHT-SIGA field areinput into the encoder 1502 in the same code block 1504. In anotherembodiment, the contents of a UHT-SIGA field are split among multiplecode blocks 1504. The encoder 1502 encodes the one or more code blocks1504 using binary convolutional coding (BCC) with a tail bitingtechnique. In this embodiment, the bits of the tail field 810-9 of FIG.8D are available for use for other purposes (e.g., for additionalsub-fields). In the embodiment of FIG. 8G, these bits have beenrepurposed for other SIGA subfields 810-10. Thus, in various embodimentsin which a tail-biting technique is used and a tail field is not neededin the UHT-SIGA field, an additional UHT-SIGA OFDM symbol may not beneeded (e.g., one or more sub-fields that would have been included inthe additional UHT-SIGA OFDM symbol can instead be included in the tailfield of another UHT-SIGA OFDM symbol), a UHT-SIGB field may not beneeded (e.g., one or more sub-fields that would have been included inthe UHT-SIGB field can instead be included in the tail field of theUHT-SIGA field), and/or the number of UHT-SIGB OFDM symbols can bereduced (e.g., one or more sub-fields that would have been included inthe additional UHT-SIGB OFDM symbol can instead be included in the tailfield of another UHT-SIGB OFDM symbol). For example, FIG. 19Aillustrates an embodiment in which the data unit 700 of FIG. 7A omitsthe UHT-SIGA2 OFDM symbol 708-2 and thus the UHT-SIGA field 708 is onlyone OFDM symbol. In another embodiment illustrated in FIG. 19B, the dataunit 700 of FIG. 7A omits the UHT-SIGB field 714. In another embodimentillustrated in FIG. 20A, the data unit 1200 of FIG. 12 omits theUHT-SIGA2 OFDM symbol 1202-2 and thus the UHT-SIGA 1200 is only one OFDMsymbol. In another embodiment illustrated in FIG. 20B, the data unit1200 of FIG. 12 omits the UHT-SIGB field 1204-2 and thus the UHT-SIGB1204 is only one OFDM symbol. In another embodiment illustrated in FIG.21A, the data unit 1300 of FIG. 13A omits the UHT-SIGA 3 OFDM symbol1302-3 and thus the UHT-SIGA field 1302 is only two OFDM symbols. Inanother embodiment illustrated in FIG. 21B, the data unit 1300 of FIG.13A omits the UHT-SIGB field 1308. In another embodiment illustrated inFIG. 22A, the data unit 1400 of FIG. 14A omits the UHT-SIGA2 OFDM symbol1408-22 and thus the UHT-SIGA field 1408 is only one OFDM symbol. Inanother embodiment illustrated in FIG. 22B, the data unit 1400 of FIG.14A omits the UHT-SIGB field 1412.

The use of tail biting in convolutional coding reduces overhead byforcing the starting state of the encoder to be the same as the endingstate, without the penalty of the overhead bits. A convolutional codingtechnique with tail biting suitable for use in the embodiments set forthherein is described in U.S. Pat. No. 7,478,314, issued on Jan. 13, 2009,entitled “METHODS, ALGORITHMS, SOFTWARE, CIRCUITS, RECEIVERS AND SYSTEMFOR DECODING CONVOLUTIONAL CODE,” the contents of which are incorporatedherein by reference in their entirety.

In an embodiment, when the encoder 1502 receives a code block 1504, theencoder 1502 is initialized with a number of final data bits of the codeblock 1504 to set an initial state of the encoder 1502. The encoder 1502then encodes the code block 1504 using binary convolutional coding togenerate coded data. Initializing the encoder 1502 with the final bitsof the code block 1504 ensures that, at the end of each the code block1504, the encoder 1502 is at the same state as the encoder 1502 was atthe beginning of the code block 1504. In another embodiment, when theencoder 1502 receives a code block 1504, the encoder 1502 is initializedwith a number, m, of first data bits of the code block 1504 to set aninitial state of the encoder 1502. Then the remaining bits of the codeblock 1504 are input to the encoder 1502. Finally, the m first data bitsof the code block 1504 are input to the encoder 1502 and the encoder1502 outputs the coded data. Initializing the encoder 1502 with the mfirst bits of the code block 1504 and then, after inputting theremaining bits of the code block 1504, inputting the m first bits of thecode block 1504 ensures that, at the end of each the code block 1504,the encoder 1502 is at the same state as the encoder 1502 was at thebeginning of the code block 1504.

The encoder 1502 is coupled to a frequency interleaver 1504 thatinterleaves bits of an encoded stream (i.e., changes the order of thebits) to prevent long sequences of adjacent noisy bits from entering adecoder at the receiver. A constellation mapping unit 1506 maps aninterleaved sequence of bits to constellation points corresponding todifferent subcarriers of an OFDM symbol. More specifically, theconstellation mapper 1506 translates every log 2(M) into one of Mconstellation points. In one embodiment, the constellation mapping unit1506 operates according to a binary phase shift keying (BPSK) modulationscheme. In other embodiments, other suitable modulation schemes areutilized. The constellation mapping unit 1506 is coupled to a toneduplication and insertion unit 1508 that implements various duplicationand insertion techniques described below in various embodiments and/orscenarios.

The output of the tone duplication and insertion unit 1508 is presentedto a stream mapping unit 1510, according to an embodiment. In anembodiment, the stream mapping unit 1510 spreads the constellationpoints to a greater number of space-time streams. A spatial mapping unit1512 maps the space-time streams to transmit chains corresponding to oneor more available transmit antennas. In various embodiments, spatialmapping includes one or more of: 1) direct mapping, in whichconstellation points from each space-time stream are mapped directlyonto transmit chains (i.e., one-to-one mapping); 2) spatial expansion,in which vectors of constellation point from all space-time streams areexpanded via matrix multiplication to produce inputs to the transmitchains; and 3) beamforming, in which each vector of constellation pointsfrom all of the space-time streams is multiplied by a matrix of steeringvectors to produce inputs to the transmit chains.

Each output of the spatial mapping unit 1512 corresponds to a transmitchain, and each output of the spatial mapping unit 1512 is operated onby an inverse discrete Fourier transform (IDFT) unit 1514 that convertsa block of constellation points to a time-domain signal. In anembodiment, the IDFT unit 1514 is configured to implement an inversefast Fourier transform (IFFT) algorithm. Each time-domain signal isprovided to a transmit antenna for transmission.

FIG. 15B is a block diagram of an example receiver 1501 configured toreceive and process an incoming OFDM symbol, according to an embodiment.Referring to FIG. 1, the AP 14 and the client station 25-1, in oneembodiment, each includes a receiver such as the receiver 1501 in theirrespective network interfaces 16 and 27. The receiver 1501 includesdiscrete Fourier transform (DFT) units 1518. Each DFT unit operates onincoming OFDM symbols from one or more antennas using a discrete Fouriertransform to convert the symbols from a time-domain to afrequency-domain signal. The output of the DFT units 1518 is a set ofconstellation points. The receiver 1501 further includes a spatialde-mapping unit 1520, a stream de-mapping unit 1522, a tone removal unit1524, a constellation de-mapping unit 1526, and a frequencyde-interleaver 1530, each of which performs an operation that isgenerally the inverse of the spatial mapping unit 1512, the streammapping unit 1510, tone duplication and insertion unit 1508,constellation mapping unit 1506, and the frequency interleaver 1504(FIG. 15A), respectively.

According to an embodiment, the frequency de-interleaver provides codeddata to a decoder 1532. The decoder 1532 searches through all possibletrellis paths having the same initial and ending state and chooses thetrellis path with the lowest cost or lowest metric (e.g., the mostlikely path). The decoder 1532 can force the initial state to aparticular value by disallowing transitions from other states (e.g., inaccordance with certain suitable predetermined constraints), and canforce the ending state to the same value as the initial state bystarting a traceback from the state with the same value. The decoder1532 decodes the coded data to generate decoded data 1534.

FIG. 16 is a flow diagram of an example method 1600 for generating adata unit, according to an embodiment. With reference to FIG. 1, themethod 1600 is implemented by the network interface 16, in anembodiment. For example, in one such embodiment, the PHY processing unit20 is configured to implement the method 1600. According to anotherembodiment, the MAC processing 18 is also configured to implement atleast a part of the method 1600. With continued reference to FIG. 1, inyet another embodiment, the method 1600 is implemented by the networkinterface 27 (e.g., the PHY processing unit 29 and/or the MAC processingunit 28). In other embodiments, the method 1600 is implemented by othersuitable network interfaces.

At block 1602, a first field of a preamble of a data unit conforming toa first communication protocol is generated. Referring to FIG. 7, in oneembodiment, the L-SIG field 706 of the data unit 700 is generated. Inanother embodiment, another suitable first field is generated. The firstfield includes a first set of one or more information bits that indicatea duration of the data unit. The first field is formatted such that thefirst field decodable by a receiver device that conforms to a secondcommunication protocol, but does not conform to the first communicationprotocol, to determine the duration of the data unit based on the firstfield. The first set of information bits corresponds, for example, to arate subfield and a length subfield of the preamble of the data unit,wherein the rate subfield and the length subfield are generated to allowthe receiver device that conforms to the second communication protocolto compute at least an approximate duration of the data unit, in anembodiment. In another embodiment, the first set of information bitsindicate other suitable information to allow a receiver device thatconforms to the second communication protocol to determine a duration ofthe data unit.

In an embodiment, the first communication protocol is the UHTcommunication protocol and the second communication protocol is a legacycommunication protocol such as the IEEE 802.11ac Standard. In otherembodiments, the first communication protocol and/or the secondcommunication protocol is another suitable communication protocol,including communication protocol not yet defined. For example, thesecond communication protocol is the UHT communication protocol, and thefirst communication protocol is a communication protocol defining evenhigher throughputs, in some embodiments.

At block 1604, a second field of the preamble is generated. Referring toFIG. 7, in one embodiment, the UHT-SIGA field 708 of the data unit 700is generated. In another embodiment, another suitable second field isgenerated. The second field includes a second set of one or moreinformation bits that indicate to a receiver device that conforms to thefirst communication protocol that the data unit conforms to the firstcommunication protocol. The second set of one or more information isgenerated according to an error detection scheme, such as a cyclicredundancy check (CRC) scheme, not specified by the second communicationprotocol, in an embodiment. For example, the second set of informationbits is generated according to the CRC generation scheme 950 of FIG. 9A,the CRC generation scheme 960 of FIG. 9B or the CRC generation scheme970 of FIG. 9C, in some example embodiments. In other embodiments, thesecond set of one or more information bits is generated according toother suitable error detection schemes not specified by the secondcommutation protocol. Additionally or alternatively, the second set ofone or more information bits is generated to indicate a mode nosupported by the second communication protocol, such as a GID and MCScombination, or another suitable mode, not supported by the secondcommunication protocol.

At block 1608, the first field is modulated according to a modulationscheme specified for a field corresponding to the first field by thesecond communication protocol. For example, the first field ismodulating using BPSK modulation, in an embodiment. In anotherembodiment, the first field is modulated using another suitablemodulation scheme, such as Q-BPSK modulation or another suitablemodulation specified for a field corresponding to the first field by thesecond communication protocol.

At block 1610, the second field generated at block 1604 isconvolutionally coded using a tail biting technique—e.g., as describedabove in conjunction with FIG. 15.

At block 1612, the second field convolutionally coded at block 1610 ismodulated according to a modulation scheme specified for a fieldcorresponding to the second field by the second communication protocol.For example, the second field comprises two OFDM symbols, wherein thefirst OFDM symbol is modulated using Q-BPSK modulation at block 1612 andthe second OFDM symbol is modulated using BPSK modulation as specifiedby the second communication protocol, in one embodiment. In otherembodiments, the second field is modulated at block 1612 using othersuitable modulation schemes specified for a field corresponding to thesecond field by the second communication protocol.

At block 1614, the preamble of the data unit is generated to include atleast the first field and the second field. At block 1616, the data unitis generated to include at least the preamble generated at block 1614.In some embodiments, the data unit is generated to further include adata portion. When the data unit is generated to include a data portion,the data portion is generated such that the data portion conforms to thefirst communication protocol, but does not conform to the secondcommunication protocol, in some embodiments.

FIG. 17 is a flow diagram of an example method 1700, according to anembodiment. With reference to FIG. 1, the method 1700 is implemented bythe network interface 16, in an embodiment. For example, in one suchembodiment, the PHY processing unit 20 is configured to implement themethod 1700. According to another embodiment, the MAC processing 18 isalso configured to implement at least a part of the method 1700. Withcontinued reference to FIG. 1, in yet another embodiment, the method1700 is implemented by the network interface 27 (e.g., the PHYprocessing unit 29 and/or the MAC processing unit 28). In otherembodiments, the method 1700 is implemented by other suitable networkinterfaces.

At block 1702, a data unit that conforms to a first communicationprotocol or to a second communication protocol is received. In anembodiment, the data unit is received by a receiver device via acommunication channel. In an embodiment, the data unit 700 of FIG. 7 isreceived. In another embodiment, the data unit 500 of FIG. 5 isreceived. In another embodiment, another suitable data unit is received.In an embodiment, the first communication protocol is the UHTcommunication protocol and the second communication protocol is a legacycommunication protocol such as the IEEE 802.11ac Standard. In otherembodiments, the first communication protocol and/or the secondcommunication protocol is another suitable communication protocol,including communication protocol not yet defined. For example, thesecond communication protocol is the UHT communication protocol, and thefirst communication protocol is a communication protocol defining evenhigher throughputs, in some embodiments.

At block 1704, a field of a preamble of the data unit received at block1702 is decoded using a tail biting technique. Referring to FIG. 7, inan embodiment, the UHT-SIGA field 708 of the data unit 700 is decodedusing a tail biting technique. Referring to FIG. 5, the VHT-SIGA field508 is decoded using a tail biting technique, in another embodiment. Inanother embodiment, another suitable field of a preamble of the dataunit received at block 1702 is decoded using a tail biting technique. Inan embodiment, decoding the field at block 1704 includes decoding areceived CRC included in the field decoded at block 1704.

At block 1706, a first CRC is generated based on the field decoded atblock 1704. The first CRC is generated using a first CRC generationscheme, the first CRC generation scheme specified for the field by thefirst communication protocol. For example, the first CRC is generatedaccording to the CRC generation scheme 950 of FIG. 9A, the CRCgeneration scheme 960 of FIG. 9B or the CRC generation scheme 970 ofFIG. 9C, in some example embodiments. In other embodiments, the firstCRC is generated according to other suitable CRC generation schemesspecified for the field by the first communication protocol.

At block 1708, a second CRC is generated based on the field decoded atblock 1704. The second CRC is generated using a second CRC generationscheme, the second CRC generation scheme specified for the field by thesecond communication protocol. For example, the second CRC is generatedaccording to the CRC generation scheme specified for the VHT-SIGA fieldin the IEEE 802.11ac Standard, in one embodiment. In other embodiments,the second CRC is generated according to other suitable schemesspecified for the field by the second communication protocol.

At block 1710, the first CRC generated at block 1706 and the second CRCgenerated at block 1708 are compared to the received CRC decoded atblock 1704. At block 1712, it is determined whether the first generatedCRC or the second generated CRC matches the received CRC. When it isdetermined at block 1712 that the first generated CRC matches thereceived CRC, the method continues at block 1714, where it is determinedthat the data unit received at block 1702 conforms to the firstcommunication protocol. On the other hand, when it is determined atblock 1712 that the second generated CRC matches the received CRC, themethod continues at block 1716, where it is determined that the dataunit received at block 1702 conforms to the second communicationprotocol.

FIG. 18 is a flow diagram of an example method 1800 for generating adata unit that conforms to a first communication protocol, according toan embodiment. With reference to FIG. 1, the method 1800 is implementedby the network interface 16, in an embodiment. For example, in one suchembodiment, the PHY processing unit 20 is configured to implement themethod 1800. According to another embodiment, the MAC processing 18 isalso configured to implement at least a part of the method 1800. Withcontinued reference to FIG. 1, in yet another embodiment, the method1800 is implemented by the network interface 27 (e.g., the PHYprocessing unit 29 and/or the MAC processing unit 28). In otherembodiments, the method 1800 is implemented by other suitable networkinterfaces.

At block 1802, a preamble of the data unit is generated. In anembodiment, the preamble of the data unit 1300 in FIG. 13 is generated.In another embodiment, another suitable preamble is generated. Thepreamble includes a first field having a plurality of OFDM symbols. Inan embodiment, the first field is the signal field 1302 in FIG. 13. Inanother embodiment, the first field is another suitable first field. Thefirst field includes at least a first OFDM symbol, a second OFDM symbol,and a third OFDM symbol.

The first OFDM symbol is convolutionally coded using a tail bitingtechnique. The first OFDM symbol is formatted such that the first OFDMsymbol is decodable by a receiver device that conforms to a secondcommunication protocol, but does not conform to the first communicationprotocol, to determine that the data unit conforms to a thirdcommunication protocol. The first OFDM symbol is formatted, for example,as the UHT-SIGA1 1302-1 of FIG. 13, in an embodiment. In thisembodiment, the first OFDM symbol is modulated according to BPSKmodulation. In an embodiment, BPSK modulation of the first OFDM symbolcauses a device that conforms to the second communication protocol(e.g., a legacy client station that conforms to the IEEE 802.11nStandard), to determine that the data unit conforms a thirdcommunication protocol (e.g., the IEEE 802.11a Standard).

In an embodiment, the second OFDM symbol is convolutionally coded usinga tail biting technique. In another embodiment, the second OFDM symbolis not convolutionally coded using a tail biting technique. The secondOFDM symbol is formatted such that the second OFDM symbol and the firstOFDM symbol are decodable by a receiver device that conforms to a fourthcommunication protocol, but does not conform to the first communicationprotocol, to determine that the data unit conforms to the thirdcommunication protocol. The second OFDM symbol is formatted, forexample, as the UHT-SIGA2 1302-2 of FIG. 13, in an embodiment. In thisembodiment, the second OFDM symbol is modulated according to BPSKmodulation. In an embodiment, BPSK modulation of the first OFDM symbol,in combination with BPSK modulation of the first OFDM symbol, causes adevice that conforms to the fourth communication protocol (e.g., alegacy client station that conforms to the IEEE 802.11ac Standard), todetermine that the data unit conforms the third communication protocol(e.g., the IEEE 802.11a Standard).

In an embodiment, the third OFDM symbol is convolutionally coded using atail biting technique. In another embodiment, the third OFDM symbol isnot convolutionally coded using a tail biting technique. The third OFDMsymbol is formatted such a receiver device that conforms to the firstcommunication protocol can determine that the data unit conforms to thefirst communication protocol. The third OFDM symbol is formatted, forexample, as the UHT-SIGA3 1302-3 of FIG. 13, in an embodiment. In thisembodiment, the third OFDM symbol is modulated according to Q-BPSKmodulation. In an embodiment, Q-BPSK modulation of the third OFDM symbolcauses a device that conforms to the first communication protocol (e.g.,the UHT communication protocol), to determine that the data unitconforms the first communication protocol.

At block 1804, the data unit is generated to include at least thepreamble. In an embodiment, the data unit 1300 of FIG. 13 is generated.In an embodiment, the data unit 1300 is generated, wherein the data unit1300 omits the data portion 716. In another embodiment, the data unit1300 is generated, wherein the data unit 1300 includes the data portion716. In other embodiments, other suitable data units are generated. Whenthe data unit is generated to include a data portion, the data portionis generated such that the data portion conforms to the firstcommunication protocol, and does not conform to either of the secondcommunication protocol, the third communication protocol, and the fourthcommunication protocol, in some embodiments.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for generating a physical layer (PHY)data unit for transmission via a communication channel, the PHY dataunit conforming to a first communication protocol, the methodcomprising: generating, at a communication device, a first field to beincluded in a PHY preamble of the PHY data unit, wherein the first fieldincludes a first set of one or more information bits that indicate aduration of the PHY data unit, the first field being formatted such thatthe first field is decodable by a receiver device that conforms to asecond communication protocol, but does not conform to the firstcommunication protocol, to determine the duration of the PHY data unitbased on the first field; generating, at the communication device, asecond field to be included in the PHY preamble, wherein the secondfield includes a second set of one or more information bits thatindicate to a receiver device that conforms to the first communicationprotocol that the PHY data unit conforms to the first communicationprotocol, and wherein generating the second field includes generatingthe second set of one or more information bits according to an errordetection scheme not specified by the second communication protocol tosignal to receiver devices that conform to the first communicationprotocol that the PHY data unit conforms to the first communicationprotocol; wherein generating the second set of one or more informationbits according to the error detection scheme not specified by the secondcommunication protocol includes: generating a plurality of cyclicredundancy check (CRC) bits for a CRC for the second field, and usingonly a subset of the plurality of CRC bits for the CRC for the secondfield, wherein using only a subset of the CRC bits for the second set ofone or more information bits preserves one or more bits of the secondset of one or more information bits that would otherwise be used for theCRC of the second field for additional signaling information for areceiver device that conforms to the first communication protocol;modulating, at the communication device, the first field using amodulation scheme specified for a field corresponding to the first fieldby the second communication protocol; convolutionally coding, at thecommunication device, the second field using a tail biting technique sothat the second field omits a tail subfield, wherein using the tailbiting technique preserves bits that would otherwise be needed for thetail subfield for additional signaling information for a receiver devicethat conforms to the first communication protocol; modulating, at thecommunication device, the convolutionally coded second field using amodulation scheme specified for a field, which corresponds to the secondfield, by the second communication protocol; generating, at thecommunication device, the PHY preamble to include at least the firstfield and the second field; generating, at the communication device, thePHY data unit to include at least the PHY preamble; and transmitting,from the communication device, the PHY data unit that includes at leastthe PHY preamble.
 2. A method according to claim 1, whereinconvolutionally coding the second field using a tail biting techniquecomprises: initializing an encoder of the communication device with oneor more last bits of a block of data that includes the second field,inputting the block of data that includes the second field into theencoder, and convolutionally coding the block of data that includes thesecond field using the initialized encoder.
 3. A method according toclaim 1, wherein generating the plurality of CRC bits comprisesgenerating the plurality of CRC bits according to a CRC polynomialdifferent than a CRC polynomial specified for the corresponding field bythe second communication protocol.
 4. A method according to claim 1,wherein generating the second set of one or more information bitsaccording to the error detection scheme not specified by the secondcommunication protocol comprises: generating the plurality of CRC bitsaccording to a CRC polynomial specified for the corresponding field bythe second communication protocol, and encrypting one or more bits ofthe subset of the plurality of CRC bits to generate the CRC for thesecond field.
 5. A method according to claim 1, wherein generating thesecond set of one or more information bits according to the errordetection scheme not specified by the second communication protocolcomprises: selecting the subset of the plurality of CRC bits, andencrypting one or more bits in the selected subset of the plurality ofCRC bits to generate the CRC for the second field.
 6. A method accordingto claim 1, wherein the second field further includes an indication thatthe PHY data unit conforms to the first communication protocol.
 7. Amethod according to claim 6, wherein the first communication protocol isa communication protocol that supports a maximum data throughput higherthan a maximum data throughput specified in the IEEE 802.11ac Standard.8. A method according to claim 1, wherein the second communicationprotocol conforms to the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11ac Standard.
 9. A method according to claim 1,wherein generating the second field includes generating the second setof one or more information bits to indicate a mode not supported by thesecond communication protocol to signal to receiver devices that conformto the first communication protocol that the PHY data unit conforms tothe first communication protocol.
 10. A method according to claim 9,wherein the second field includes a modulation and coding (MCS)subfield, and wherein generating the second set of one or moreinformation bits to indicate the mode not supported by the secondcommunication protocol includes generating the MCS subfield to indicatea modulation and coding scheme not supported by the second communicationprotocol.
 11. An apparatus comprising: a network interface devicecomprising: a physical layer (PHY) processing unit implemented using oneor more integrated circuits, the PHY processing unit configured togenerate PHY data units for transmission in a wireless communicationnetwork, and a medium access control (MAC) processing unit implementedusing one or more integrated circuits, the MAC processing unit coupledto the PHY processing unit; wherein the PHY processing unit isconfigured to: generate a first field to be included in a physical layer(PHY) preamble of a PHY data unit, wherein the first field includes afirst set of one or more information bits that indicate a duration ofthe PHY data unit, the first field being formatted such that the firstfield is decodable by a receiver device that conforms to a secondcommunication protocol, but does not conform to the first communicationprotocol, to determine the duration of the PHY data unit based on thefirst field, generate a second field to be included in the PHY preamble,wherein the second field includes a second set of one or moreinformation bits that indicate to a receiver device that conforms to thefirst communication protocol that the PHY data unit conforms to thefirst communication protocol, and wherein generating the second fieldincludes generating the second set of one or more information bitsaccording to an error detection scheme not specified by the secondcommunication protocol to signal to receiver devices that conform to thefirst communication protocol that the PHY data unit conforms to thefirst communication protocol, modulate the first field using amodulation scheme specified for a field corresponding to the first fieldby the second communication protocol, convolutionally code the secondfield using a tail biting technique, wherein using the tail bitingtechnique preserves bits that would otherwise be needed for the tailsubfield for additional signaling information for a receiver device thatconforms to the first communication protocol, modulate theconvolutionally coded second field using a modulation scheme specifiedfor a field, which corresponds to the second field, by the secondcommunication protocol, generate the PHY preamble to include at leastthe first field and the second field, and generate the PHY data unit toinclude at least the PHY preamble; and transmit the PHY data unit thatincludes at least the PHY preamble; wherein the PHY processing unit isconfigured to generate the second set of one or more information bitsaccording to the error detection scheme not specified by the secondcommunication protocol at least by: generating a plurality of cyclicredundancy check (CRC) bits for a CRC for the second field, and usingonly a subset of the plurality of CRC bits for the CRC for the secondfield, wherein using only a subset of the CRC bits for the second set ofone or more information bits preserves one or more bits of the secondset of one or more information bits for additional signaling informationfor a receiver device that conforms to the first communication protocol.12. An apparatus according to claim 11, wherein the PHY processing unitimplemented using one or more integrated circuits is configured to:initialize an encoder, implemented on the one or more integratedcircuits, with one or more last bits of a block of data that includesthe second field, input the block of data that includes the second fieldinto the encoder, and convolutionally code the block of data thatincludes the second field using the initialized encoder.
 13. Anapparatus according to claim 11, wherein the PHY processing unitimplemented using one or more integrated circuits is configured togenerate the plurality of CRC bits at least by generating the pluralityof CRC bits according to a CRC polynomial different than a CRCpolynomial specified for the corresponding field by the secondcommunication protocol.
 14. An apparatus according to claim 11, whereinthe PHY processing unit implemented using one or more integratedcircuits is configured to generate the second set of one or moreinformation bits according to the error detection scheme not specifiedby the second communication protocol at least by: generating theplurality of CRC bits according to a CRC polynomial specified for thecorresponding field by the second communication protocol, and encryptingone or more bits of the subset of the plurality of CRC bits to generatethe CRC for the second field.
 15. An apparatus according to claim 11,wherein the PHY processing unit implemented using one or more integratedcircuits is configured to generate the second set of one or moreinformation bits according to the error detection scheme not specifiedby the second communication protocol at least by: selecting the subsetof the plurality of CRC, and encrypting one or more bits in the selectedsubset of the plurality of CRC bits to generate the CRC for the secondfield.
 16. An apparatus according to claim 11, wherein the PHYprocessing unit implemented using one or more integrated circuits isconfigured to include, in the second field, an indication that the PHYdata unit conforms to the first communication protocol.
 17. An apparatusaccording to claim 11, wherein the second communication protocolconforms to the Institute for Electrical and Electronics Engineers(IEEE) 802.11ac Standard.
 18. An apparatus according to claim 17,wherein the first communication protocol is a communication protocolthat supports a maximum data throughput higher than a maximum datathroughput specified in the IEEE 802.11ac Standard.
 19. An apparatusaccording to claim 11, wherein the network interface device includes oneor more transceivers implemented on the one or more integrated circuits.20. An apparatus according to claim 19, further comprising one or moreantennas coupled to the one or more transceivers.
 21. An apparatusaccording to claim 11, wherein generating the second field includesgenerating the second set of one or more information bits to indicate amode not supported by the second communication protocol to signal toreceiver devices that conform to the first communication protocol thatthe PHY data unit conforms to the first communication protocol.
 22. Anapparatus according to claim 21, wherein the second field includes amodulation and coding (MCS) subfield, and wherein the PHY processingunit implemented using one or more integrated circuits is configured togenerate the second set of one or more information bits to indicate themode not supported by the second communication protocol at least bygenerating the MCS subfield to indicate a modulation and coding schemenot supported by the second communication protocol.